The present application claims priority to Japanese Application No. P10-116623 filed Apr. 27, 1998 which application is incorporated herein by reference to the extent permitted by law.
The present invention relates to an electromagnetic wave shielding apparatus and an electromagnetic wave shielding method used for electric circuits, electronic circuits and the like.
In electric circuit arrangements, electronic circuit arrangements and the like, it is necessary to prevent electromagnetic waves generated from electronic parts and the like installed in the circuit arrangement from being leaked to the outside. For example, a circuit board 100 of a related art electronic circuit arrangement shown in FIG. 7 has electronic parts 101 and 102 which generate electromagnetic waves 103 in the directions shown by the arrows, and which circuit board 100 is covered with a case 104. In this case, the electromagnetic waves 103 are reflected from the inner surfaces of the case 104 and leaked to the outside through a small gap 105 and/or wiring. The case 104, if being made from a metal, produces a high-frequency current when it is exposed to the electromagnetic waves, and therefore, the case 104 becomes a re-generating source of electromagnetic wave noise.
To cope with such an inconvenience, in the related art electronic circuit arrangement, as shown in FIG. 8, an electromagnetic wave absorbing member 110 is fixed on a surface, facing to the electronic parts, of the inner wall of the case 104. The electromagnetic wave absorbing member 110 functions to absorb or attenuate the electromagnetic waves 103 and prevent leakage of the electromagnetic waves 103 to the outside as much as possible, to reduce the degree of reflection of the electromagnetic waves 103 and decay the electromagnetic waves 103, and to prevent re-generating of electromagnetic wave noise from the case 104.
The related art electromagnetic wave absorbing member 110, however, has disadvantages that it takes a lot of time to lay out the member 110 because the member 110 must be stuck on the inner surface of the shield case 104 with an adhesive double coated tape or the like by an operator in such a manner as to ensure the optimum absorption of electromagnetic waves, and that the weight of the circuit board 100 becomes very large because the member 110 having a large thickness is stuck on the inner surface of the case 104 with an adhesive double coated tape or the like.
An object of the present invention is to provide an electromagnetic wave shielding apparatus and an electromagnetic wave shielding method, which are capable of simply obtaining an electromagnetic wave shielding function without increasing the weight of the apparatus.
To achieve the above object, according to a first aspect of the present invention, there is provided an electromagnetic wave shielding apparatus for shielding electromagnetic waves generated from a circuit so as to prevent the electromagnetic waves from being leaked to the outside of the circuit, including: a metal member disposed in such a manner as to be opposed to the circuit; and an electromagnetic wave absorbing member disposed on the metal member; wherein the electromagnetic absorbing member is composed of a carbon layer and coil-like carbon fiber structures.
With this configuration, since the electromagnetic wave absorbing member is composed of the carbon layer and the coil-like carbon fiber structures which are formed on the metal member, it can be made lighter than that of the related art electromagnetic wave absorbing member, and since the coil-like carbon fiber structures are electrically conductive, the electromagnetic wave absorbing member is capable of efficiently absorb electromagnetic waves generated from an electromagnetic wave generating source through the coil-like carbon fiber structures.
In the above apparatus, preferably, the carbon layer is formed on a surface, facing to the circuit, of the metal members; one-end portions of the coil-like carbon fiber structures are connected to the carbon layer; and the axial directions of the coil-like carbon fiber structures are substantially perpendicular to an electromagnetic wave generating source. With this configuration, electromagnetic waves generated from an electromagnetic wave generating source can be efficiently absorbed in the carbon layer through the coil-like carbon fiber structures.
According to a second aspect of the present invention, there is provided an electromagnetic wave shielding method for shielding electromagnetic waves generated from a circuit so as to prevent the electromagnetic waves from being leaked to the outside of the circuit, including the steps of: forming an electromagnetic wave absorbing member on a metal member; and disposing the metal member in such a manner that the metal member is opposed to the circuit; wherein the electromagnetic wave member is composed of a carbon layer and coil-like carbon fiber structures produced by a chemical vapor deposition process based on thermal decomposition.
With this configuration, the electromagnetic wave absorbing member can be simply formed on the metal member by chemical vapor deposition, being made lightweight, and is capable of efficiently absorb electromagnetic waves.
In the above method, preferably, the carbon layer is formed on a surface, facing to the circuit, of the metal members; one-end portions of the coil-like carbon fiber structures are connected to the carbon layer; and the axial directions of the coil-like carbon fiber structures are substantially perpendicular to an electromagnetic wave generating source.
With this configuration, since the electromagnetic wave absorbing member is composed of the carbon layer and the coil-like carbon fiber structures which are formed on the metal member, it can be made lighter than that of the related art electromagnetic wave absorbing member, and since the coil-like carbon fiber structures are electrically conductive, the electromagnetic wave absorbing member is capable of efficiently absorb electromagnetic waves generated from an electromagnetic wave generating source through the coil-like carbon fiber structures.
According to the present invention, a shield case for shielding a circuit can be simply prepared by working the metal member on which the electromagnetic wave absorbing member has been formed, into a desired shape.